import type { NamedCSSColour, WCAG } from "./types";
/**
 * Evaluates if a colour is dark by measuring the contrast ratio against black and white.
 * It accepts CSS RGB colours (including percentage values), named CSS or hexadecimal.
 *
 * If you know in advance the type of colour you want to evaluate consider using `isCSSNamedDarkColour`, `isCSSRGBDarkColour` or `isHexDarkColour` as they are smaller functions
 * @param {string | NamedCSSColour} colour - A colour value, ie: `hotpink`, `#333222`, `rgb(12,34,45)`, or `rgb(50%, 25%, 100%)`
 * @param {"WCAG2.1" | "WCAG3.0"} standard - Evaluate agains "WCAG2.1" or "WCAG3.0"
 * @returns {boolean} Returns `true`, `false` or `undefined` if name is not a valid CSS named colour
 */
export declare function isDarkColour(colour: string | NamedCSSColour, standard: WCAG): boolean;